Can I use ? _____Chain question

[one-eyed_jim]

No problem. I've been running SRAM PC59 chains on a 7-speed STX bike for years. Shifting's fine.

 

[Anthony]

You can't use a 7/8-speed chain on a 9-speed set up because it's too wide for the gaps in the cassette so it's liable to foul the next biggest sprocket. But there's nothing to stop you using a 9-speed chain on a 7/8-speed set up.

 

[Russell]

I use 9spd chains on all my bikes, including the ones with 7spd cassettes. No problems at all.